How a series of physical and chemical events leads to a very non physical/ intangible perception? For example, let's say a certain wavelength of light falls on the retina of my eyes, then the sensory cells convert that into electrical signals that go to the brain through optic nerves and there it leads to a series of chemical activities that makes us perceive a certain colour, say red. But there is no such thing as red or blue or green or yellow or anything else outside of our brains. These perception of colours or perceptions in general aren't absolute, they don't exist without us. Heck, we can't even know that how i perceive red is same as how others perceive red. So, how do we perceive a sensation? What are our perceptions? Can it be even explained by science?